[clang] do not limit -fstack-clash-protection to Linux

[emaste]

Summary

The feature does not have an OS dependency.

See also D68720 and https://reviews.freebsd.org/D27366

[emaste]

clang/test/Driver/stack-clash-protection.c

21–23

Likely FileCheck tag should be something like SCP-enabled shared between x86_64-pc-unknown-linux and x86_64-unknown-freebsd13.

[rnk]

lgtm

clang/lib/Driver/ToolChains/Clang.cpp

3086

IMO this comment would help. I had forgotten System Z is an architecture.

[MaskRay]

clang/test/Driver/stack-clash-protection.c

21–23

For compile actions not related to linking, you can change the target triple to -target x86_64 (generic ELF) to represent that both Linux/FreeBSD work.

[emaste]

• add comment suggested by @rnk
• combine Linux and FreeBSD FileCheck

[emaste]

clang/test/Driver/stack-clash-protection.c

21–23

What would isOSLinux or isOSFreeBSD return in that case - does it depend on the platform running the test, or they'd both always be false, for generic?

[MaskRay]

clang/test/Driver/stack-clash-protection.c

21–23

Both isOSLinux or isOSFreeBSD return false. For functionality features, if generic ELF works, I'd expect it work for Linux/FreeBSD and probably other ELF based OSes as well.

[serge-sans-paille]

The backend implementation of stack-clash-protection is incompatible with Windows, see https://github.com/llvm/llvm-project/blob/master/llvm/lib/Target/X86/X86FrameLowering.cpp#L486

cpp
void X86FrameLowering::emitStackProbe(MachineFunction &MF,
                                      MachineBasicBlock &MBB,
                                      MachineBasicBlock::iterator MBBI,
                                      const DebugLoc &DL, bool InProlog) const {
  const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
  if (STI.isTargetWindowsCoreCLR()) {
    if (InProlog) {
      BuildMI(MBB, MBBI, DL, TII.get(X86::STACKALLOC_W_PROBING))
          .addImm(0 /* no explicit stack size */);
    } else {
      emitStackProbeInline(MF, MBB, MBBI, DL, false);
    }
  } else {
    emitStackProbeCall(MF, MBB, MBBI, DL, InProlog);
  }
}

This is possibly addressed by https://reviews.llvm.org/D92245 though.

[emaste]

Perhaps

if (EffectiveTriple.isOSWindows() || EffectiveTriple.isOSDarwin())
  return;

here too

[emaste]

Abandon in favour of D92245

clang/lib/Driver/ToolChains/Clang.cpp

if (Arg *A = Args.getLastArg(options::OPT_mstack_protector_guard_reg_EQ)) {
     A->render(Args, CmdArgs);
   }
 }
 
 static void RenderSCPOptions(const ToolChain &TC, const ArgList &Args,
                              ArgStringList &CmdArgs) {
   const llvm::Triple &EffectiveTriple = TC.getEffectiveTriple();
 
-  if (!EffectiveTriple.isOSLinux())
-    return;
-
+  // Only enable stack clash protection for backends that implement it.
   if (!EffectiveTriple.isX86() && !EffectiveTriple.isSystemZ() &&
       !EffectiveTriple.isPPC64())
     return;
 
   if (Args.hasFlag(options::OPT_fstack_clash_protection,
                    options::OPT_fno_stack_clash_protection, false))
     CmdArgs.push_back("-fstack-clash-protection");
 }

clang/test/Driver/stack-clash-protection.c

 // RUN: %clang -target armv7k-apple-linux -fstack-clash-protection -### %s 2>&1 | FileCheck %s -check-prefix=SCP-armv7
 // SCP-armv7-NOT: "-fstack-clash-protection"
 // SCP-armv7: argument unused during compilation: '-fstack-clash-protection'
 
 // RUN: %clang -target x86_64-unknown-linux -fstack-clash-protection -S -emit-llvm -o %t.ll %s 2>&1 | FileCheck %s -check-prefix=SCP-warn
 // SCP-warn: warning: Unable to protect inline asm that clobbers stack pointer against stack clash
 
 // RUN: %clang -target x86_64-pc-unknown-linux -fstack-clash-protection -S -emit-llvm -o- %s | FileCheck %s -check-prefix=SCP-ll-linux64
-// SCP-ll-linux64: attributes {{.*}} "probe-stack"="inline-asm"
+// RUN: %clang -target x86_64-unknown-freebsd13 -fstack-clash-protection -S -emit-llvm -o- %s | FileCheck %s -check-prefix=SCP-inline-asm
+// SCP-inline-asm: attributes {{.*}} "probe-stack"="inline-asm"
 
 // RUN: %clang -target x86_64-pc-windows-msvc -fstack-clash-protection -S -emit-llvm -o- %s 2>&1 | FileCheck %s -check-prefix=SCP-ll-win64
 // SCP-ll-win64-NOT: attributes {{.*}} "probe-stack"="inline-asm"
 // SCP-ll-win64: argument unused during compilation: '-fstack-clash-protection'
 
 int foo(int c) {
   int r;
   __asm__("sub %0, %%rsp"
           :
           : "rm"(c)
           : "rsp");
   __asm__("mov %%rsp, %0"
           : "=rm"(r)::);
   return r;
 }